• Macromolecular Research
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• 제12권5호
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• pp.490-492
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• 2004

We report a new method using a heating medium for the thermal decomposition of epoxy resin (EP) at temperatures ranging from 50 to 200$^{\circ}C$. EP decomposition also occurred below 50$^{\circ}C$ during a 6-day period to generate bisphenol A (BPA) at concentrations as high as 5 ppm. When polyethylene glycol was used as a heating medium, we determined the kinetics of the EP decomposition at low temperature. We determined the apparent activation energy of the overall decomposition to be 40.8 kJ/mol and the frequency factor to be 2.3${\times}$10$^3$ by monitoring the rate of BPA formation. Thus, EP is clearly unstable upon the application of heat.

• Advances in Traditional Medicine
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• 제4권4호
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• pp.227-234
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• 2004

An ${\alpha}-Amylase$ was purified to apparent homogeneity from germinating soybean seeds (Glycine max). Enzyme showed high specificity for starch. ${\alpha}-Amylase$ from soybean has optimum pH at 7.6 in the pH range 4.0-10.6. At this pH, the $K_m$ of starch was 2.63 mg/ml and the $V_{max}$ was equal to 52.6 mg/ml/min protein. Optimum temperature of the enzyme was found to be $55^{\circ}C,\;Q_{10}$ equal to 1.85 and energy of activation equal to 12 kcal/mol. Additives like, EDTA reduced the activity of ${\alpha}-amylase$ whereas PMSF enhanced the activity. ${\alpha}-Amylase$ was inhibited by several heavy metal ions.

• 한국세라믹학회지
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• 제33권9호
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• pp.985-994
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• 1996

The initiation and growth of $\alpha$-Al2O3/metal composites by the directed oxidation of molten commercial AlZnMg-alloy at 1223-1423K were investigated. Spontaneous bulk growth did not occur on the alloy alone. but the uniform initiation and growth of the composite were obtained by putting a thin layer of SiO2 particles on the surface of the alloy. Without SiO2 the external surface of the oxide layer was convered by MgO and MgAl2O4. But with the SiO2 reaction initiate the porous ZnO layers were found on the growth surface. The higher process temperature yielded a lower metal content. The oxidation product of $\alpha$-Al2O3 was found to be oriented with c-axis parallel to th growth direction. The growth rates increased with temperature and the apparent activation energy was 111.8 kJ/mol.

• 한국세라믹학회지
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• 제28권1호
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• pp.1-10
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• 1991

Zirconium dioxide(ZrO2) thin films have been deposited by chemical vapor deposition technique involving the application of gas mixture of ZrCl4, and H2O into silicon wafers. The relationships between the deposition rate and various reaction parameters such as the deposition time, the gas flow rate, the deposition temperature, and the composition of reactant gases were studied. The film was identified as nearly stoichiometric monoclinic ZrO2. The apparent activation energy is about 19Kcal/mole at surface chemical reaction controlled region. The deposition rate is mainly influenced by the H2O-forming reacting between CO2 and H2.

• 한국세라믹학회지
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• 제25권2호
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• pp.184-190
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• 1988

ZrN powder was prepared from the powder mixture of ZrCl4 and Al by the halogenide process in nitrogen gas flow (100-150ml/min) at the temperatures from 200$^{\circ}$to 1050$^{\circ}C$. ZrN powder was formed about 600$^{\circ}C$ and in the slow nitriding reaction, however, an intermediate product of Al3Zr was formed. The fine powder (0.1-10$\mu\textrm{m}$) of single phase ZrN was obtained at 1050$^{\circ}C$ after 1 hour. The lattice parameter and crystallite size of ZrN were 4.5787A and 360A, respectively. According to SEM observation, the particles were apt to agglomerates. The apparent activation energy for the formation of ZrN was approximately 13.2kcal/mole(750$^{\circ}$-1000$^{\circ}C$).

• 한국안전학회지
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• 제7권1호
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• pp.47-56
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• 1992

Spontaneous ignition charactenstics for fish meal were observed by performing experiments at constant ambient temperature and varying the ambient temperature sinusoidally. As the results of the experiments at a constant ambient temperature, the critical spontaneous ignition temperature of the sample for large, intermediate and small vessels was 170.5$^{\circ}C$, 177.5$^{\circ}C$ and 188.5$^{\circ}C$, respectively. The critical spontaneous ignition temperature decreased as the sample vessel size increased. Apparent activation energy of used fish meal calculated from the Frank-Kamenetskii's thermal ignition theory was 37.60Kcal/mol. In case of varying the ambient temperature sinusoidally, the amplitudes of temperature were 1$0^{\circ}C$, 2$0^{\circ}C$ and 3$0^{\circ}C$ respectively with the period in each amplitude 1hr, 2hrs and 3hrs. The results showed that the critical spontaneous ignition temperatures at the varied amplitudes of temperature were lower than that at the constant anbient temperature and increased as the amplitude increased. At the same amplitude, the critical spontaneous ignition temperature increased with the period.

• Macromolecular Research
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• 제8권4호
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• pp.147-152
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• 2000

The activity of periodic acid as an initiator for the polymerization of acrylamide in aqueous medium was investigated. The rate of polymerization was found to be proportional to the monomer concentration to the 1.5th power in the range of 1.41-5.64 mol/L. The reaction order to the periodic acid concentration was 0.49, which indicated a bimolecular mechanism for the termination reaction in the range of 0.5-4.0$\times$10$\^$-2/ mol/L. Propagation rate increased with raising the temperature according to an Arrhenius expression resulting in the exhibition of an apparent activation energy of 87.8 kJ/mol in the temperature range of 60-80$\^{C}$. The addition of hydroquinone as a radical scavenger stopped the polymerization of acrylamide initiated by periodic acid. These results support that the polymerization proceeds via a radical chain mechanism .

• 한국세라믹학회지
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• 제27권5호
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• pp.652-660
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• 1990

Oxidation of Mn-Zn ferrite was made in air at various temperatures ranging from 400$^{\circ}C$ to 1150$^{\circ}C$. Subsequent reduction fo these oxidized samples was also made in air at 1300-1350$^{\circ}C$ where the spinel phase of Mn-Zn ferrite is stable. Morphological observation revealed that the shape of precipitated hematite was plate or lath type on the close-packed habit plane of {111} ferrite which has a definite orientation relationship. The growth of precipitates showed the behavior fo parabolic dependence of the oxidating time. An apparent activation energy for the growth was found to be 125${\pm}$3Kcal/mol. The fact that pores are observed along the precipitates illustrates the oxidation to occur dominantly by the counterdiffusion of cations and ction vacancies. For the reductio reaction pores are found to form at the site once occupied by the precipitates and at the surface. This observation illustrates that the oxygen volitalization from interior region to the surface is the dominant process for the reduction reaction.

• Journal of Pharmaceutical Investigation
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• 제18권4호
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• pp.203-208
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• 1988

The stability and solubility of piroxicam in propylene glycol (PG), polyethylene glycol (PEC), and PG-water cosolvents have been studied by using high performance liquid chromatography. The degradation rate followed an apparent first-order kinetic and the reaction rate constants at 70, 80, and $90^{circ}C$ were determined. From these rate constants, the activation energy and the rate constant of piroxicam at $25^{circ}C$ in pure PG calculated by Arrhenius equation were 23.34 kcal/mole and $7.0\;{\times}\;10^{-4}\;day^{-1}$, respectively. Both of PG and PEG increased the solubility of the drug, but PEG was more effective.

• 한국표면공학회지
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• 제18권3호
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• pp.116-124
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• 1985

Chemical vapor deposition of $SnO_2$ on Pyrex glass substrate has been investigated using $SnCl_4$ and Oxygen at relatively low temperatures(300-500$^{\circ}C$). The critical flow rate, which delineated the surface reaction controlled region from the mass transfer controlled region, was increased with deposition temperature. The apparent activation energy obtained in surface reaction controlled region was about 6Kcal/mole. The results show that deposition rate, electrical conductivity and transmittance were affected mainly by partial pressure of $SnCl_4$, but little by partial pressure f oxygen. The % transmission of 5000A-thick $SnO_2$ film was about 90% in visible spectrum region and sheet resistance was varied in 0.1-10${\Omega}$ per square shaped portion of the outer surface of the oxide.